1. Field of the Invention
This invention relates generally to transceiver systems and methods, and more particularly to a technique for solving transmitter impairments when a system has both receiver and transmitter operating with the same local oscillator frequency but with independent phase and gain impairments.
2. Description of the Prior Art
Schemes utilizing the complex conversion (down conversion or up conversion) use two local oscillators (shifted by 90 degrees) and two mixers to form two orthogonal output signals in down conversion. One is referred to as Real and the other as Imaginary. In the up conversion case the complex baseband signal is up converted to a real signal in IF. Implementing this scheme using analog components (phase shifter and mixer) causes phase, gain and delay mismatches. The delay mismatch can be regarded as phase mismatch as long as the signal bandwidth is relatively small with respect to its center frequency.
Some systems include both a transmitter and a receiver operating in conjunction with the respective local oscillators and having the same frequency but with independent phase and gain errors. Such system exist for example in the case of Wireless Local Area Network WLAN Institute of Electrical and Electronics Engineers (IEEE 802.11), where possible implementation includes a complex up converter and a complex down converter, both having the same local oscillator frequency. This approach, being low cost and simple, is widely used in many applications such as the Wireless Local Area Network WLAN. Each of the converters needs the phase and gain mismatch to be corrected in case of limited analog performance of the converters. Each one must be optimized independently, as transmitter and receiver specifications are set separately due to interoperability requirements between different vendors.
In view of the foregoing, a need exists for a technique to solve transmitter impairments when a system has both receiver and transmitter operating with the same local oscillator frequency but with independent phase and gain impairments.